Superficial zone

PRG4 Proteoglycan 4 (megakaryocyte-stimulating factor articular superficial zone protein)... 

Figure 3.23. Diagram illustrating the zonal structure of articular cartilage. The superficial zone contains aligned collagen fibrils the intermediate zone contains unoriented collagen fibrils the deep zone contains collagen fibrils perperdicular to the subchondral bone.

Figure 9.6. Diagram illustrating the pretension present in the superficial zone of articular cartilage. Normal articular cartilage shown at the top is loaded in tension across the surface like a drumhead that is pulled taut over a drum. When a piece of cartilage is cut from the surface, it curls as a result of release of this tension, as shown in the lower diagram. The presence of tension in the superficial zone makes articular cartilage behave like a drumhead, allowing compressive forces applied to the surface at specific points to be distributed across the surface to lower local stresses. The presence of tension on the chondrocytes in the superficial layer may be important to limit inflammation and support reparative processes by stimulating mechanochemical transduction.

Wise JK et al (2009) Chondrogenic differentiation of human mesenchymal stem cells on oriented nanofibrous scaffolds engineering the superficial zone of articular cartilage. Tissue Eng A 15(4) 913-921... 

The superficial zone contains the highest density of chondrocytes, with the type II collagen fibers being oriented parallel to the joint surface. 

To understand the burning of polymers better, the combustion region may be divided into five zones, as shown in Figure 5.1. The first zone is defined by the polymer layer where pyrolysis takes place due to heat produced in the flame, but very little oxidation takes place. Thermal oxidation takes place in the second superficial zone. In the third zone, which is a gaseous one, low-molecular-weight products formed in these two zones are mixed with heated air and are decomposed or oxidized by oxygen or by radicals coming out of the flame. 

The overall structure of articular cartilage is analogous to a jelly-filled balloon. The PG-rich middle zone is osmotically pressurized, with fluid restrained from exiting the tissue by the dense coUagen network of the superficial zone and the calcified structure of the deep bone. The interaction between the mechanical loading forces and osmotic forces yields the complex material properties of articular cartilage. 

Since hydrogen peroxide generated within the mitochondria of chondrocytes can freely permeate through the chondrocyte cell wall, one should admit the presence of in nil (deep, middle, and superficial) zones of the articular cartilage (Figure 4). The higher the tension, the greater is the content of H Oj and vice-versa. 

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